Throughout history, wastewater has been an unavoidable consequence of man's existence on the earth, and one which has been compounded by the growth of the human population, the development of an industrial society and the exploitation of fossil fuels.
Some of the most challenging problems in the world today are the large volumes of contaminated water that are part of the waste streams of rural and urban societies. These waste streams exist in large volumes in every established and emerging setting in the world. Typical are the United States and China, both having nearly insurmountable problems processing Municipal Solid Waste, biological or sewer wastewater and industrial waste while exhausting their supplies of potable or fresh water.
As can be seen by the most recent United States patent filings which come from all over the world's developed and emerging societies, there is an extreme focus on dewatering sludge of various types, from sewer sludge to industrial waste sludge to oil field sludge.
Yongfeng He, in his Oct. 23, 2013, U.S. Pat. No. 8,561,319 B2, disclosed a system that uses a series of centripetal fans to accelerate raw wet sludge that has been driven through hammer wheels to reduce the particle size to collide with previously dehydrated sludge which is now a dry powder. The resulting product is allowed to settle in a room where the air is vented away. If there is a requirement for very dry powder, then this process is repeated up to three times. This system is a fully automated system designed to operate continuously.
Very few months after Mr. He's patent, Ming Lu was granted U.S. Pat. No. 8,691,094 B2 for teaching a method of simultaneously processing Organic Municipal Solid Waste and municipal sewage in a process where the combined inner process products are used to increase the effectiveness of the process. Lu's patent discloses a mechanically enhanced biological process.
Huansheng Zhong's U.S. Pat. No. 8,808,419 discloses a method that prescribes conditioning cycles using both organic agents and an inorganic agent of Fe3+. The mixture is mechanically dehydrated in a press. The clumps are forcibly broken up and then dried using air as the mixture is mechanically turned over. The resulting exothermic reaction drives the moisture out of the sludge, after which the mixture can be sterilized by various methods.
Richard Kuper in his U.S. Pat. No. 9,327,997 B1 presents a method of using a vacuum to depress the boiling point of the water in the sludge which is moved through an apparatus with rotary meter vacuum valves. The vaporized water is condensed down process and the heat of condensation is captured and used to heat the incoming sludge prior to entering the evaporation stage.
In contrast, Kaoru Yamaguchi's U.S. Pat. No. 9,364,837 B2 uses a centripetal device to remove moisture by centrifugal forces. The specific feature of this horizontal straight drum is the improvement of two different tapered sections plus the addition of an inorganic flocculent injection system. The straight drum flows into a gently tapered section, which flows into a much steeper tapered section where a build-up of cake creates a resistance path adding another dimension to the compression of the cake. According to Mr. Yamaguchi, his apparatus and the improved method of implementation greatly improve the moisture reduction over existing processes and machines.
In U.S. Pat. No. 9,381,711 B2, Jeong Oh presents a novel screw compressor dehydrating device which essentially slices the wet sludge in advancing microscopic increments with the goal of rupturing the physical structure of the microbes that physically make up the principal mass of the sewer sludge material. The water content of the sludge is trapped inside the physical structure of the microbes. Rupturing them releases the water.
Inventor Artur Zimmer, in his US Patent application number US 2017/0028310 A1, presents a mobile mechanical vapor recompression system targeting the reduction of Total Dissolved Solids (TDS) in wastewater (e.g., frac water) through a reduced-pressure distillation process. This system targets TDS in the range of 150,000 mg/L and produces concentrate product in the 200,000 to 300,000 mg/L range. The goal is a condensate product with TDS below 300 mg/L. A Mechanical Vapor Re-compression system is presented that solves the problem of the rising concentrate boiling point as the TDS increases. The system can split into two systems and dilute the concentrate with additional intake wastewater.
Each of these referenced patents presents a clearly different approach to the dehydration challenge of wastewater and/or sludge drying. Their reference is important to present as background to this inventor's disclosure of this unique thermal energy transfer method and supporting dehydrator apparatus.
Although the referenced patents are a survey of the state-of-the-practice, none of them apply Mechanical Vapor Re-compression (MVR) to the process of drying sludge when the moisture content of the sludge is less than about 85%. In fact, an extensive survey of operational systems reported in the popular literature has not revealed the use of MVR technologies when the moisture content is less than about 96%. This disclosure presents a method that exploits the highly efficient MVR process applied “adaptively” to sludge dehydration with moisture contents of the input feed material from 99% to less than 20%; yet the system is designed to output material with moisture contents of less than 5%.
Most common forms of waste material are laden with liquid. Such materials may be mud composed of water and soil, petroleum sludge composed of water and petroleum solids and (probably) soil and sewer sludge composed of animal and/or human waste and water.
Currently, the most efficient process for extracting a highly homogenous product from a liquid composed of suspended solids, some dissolved materials and/or some highly absorbent organic material is reverse osmosis using the rapidly advancing membrane technology. But membrane filters, polymer or ceramic, are only useful if the fluid is nearly homogenous with a small solids component. Clogging and scheduled maintenance intervals drive up costs and limit equipment availability.
The energy use is an issue when processing sludge-like materials, as the typical process in use worldwide is to apply energy as mechanical force, such as a screw compressor or a centrifuge, to reduce the moisture in the sludge before subjecting the sludge (which still contains as much as 80% water) to an evaporative cycle. Typical thermal processes involve heating at environmental atmospheric pressure to evaporate the remaining water or depositing the sludge on the ground and letting it dehydrate naturally, ignoring the potential for harm due to possible biological components.
All known MVR technologies as applied to water-based waste streams are designed around the specific heat and latent heat of a feedstream that is more than 96% water. The disclosure herein reveals a method and a supporting apparatus that adaptively reconfigure the key operational parameters of a Mechanical Vapor Re-compression (MVR) process to appropriate values for optimized processing based on the composite specific heat and the mass of the input feedstream, the latent heat of the liquid component of the feedstream and the boiling point of that liquid.
The spawn of urbanization and industrialization include not only waste products such as Municipal Solid Waste (MSW) which is typically between five and forty percent water, but other bio-solids, including sewer sludge, agricultural waste, wood waste, food waste, slaughterhouse waste and even fish processing waste, among others which all typically contain a significant liquid component.
The Adaptive Mechanical Vapor Re-compression (AMVR) process disclosed herein has the potential to save energy by improving the efficiency of many industrial processes that involve removing the liquid component from a composite semi-solid with a sludge-like consistency.
It is the current state of the practice and common in utility fields for the system designs and the build methods to involve large steel (thermal conductivity of approximately 42 W/m-C.°) or stainless steel (thermal conductivity of approximately 16 W/m-C.°) tanks with high water (thermal conductivity of approximately 0.58 W/m-C.°) volumes, all of which are barriers to heat flow. The improved method disclosed herein of heating to vaporize the liquid component in sludge material involves a manipulation of the Ideal Gas Law (i.e., PV=nRT) and an apparatus optimized for thermal conductivity so constructed as to minimize the heat flow path through the composite or sludge material itself.